Composition and method of inhibiting corrosion of copper-containing metals



United States Patent ()fliice 3,247,124 Patented Apr. 19, 1966COMPOSITION AND METHOD OF INHIBIT- ING CORROSION F COPPER-CONTAIN- INGMETALS Robert C. Kimble, John B. Braunwarth, and Louis A. J00, CrystalLake, 11]., assignors, by mesne assignments, to Union Oil Company ofCalifornia, Los Angeles, Calif., a corporation of California No Drawing.Filed July 11, 1962, Ser. No. 209,256 9 Claims. (Cl. 252-138) Thisinvention relates to a method for inhibiting corrosive attack uponcopper alloys contacted by aerated, aqueous detegrent solutions, and toa novel detergent composition.

Copper alloys such as brasses and bronzes usually display highresistance to corrosive attack by water or aerated, aqueous saltsolutions. Copper alloys which are highly resistant to corrosive attack,such as admiralty brass, nevertheless have been found to be rapidlycorroded when contacted by aerated, aqueous solutions of commercialdetergents. The art recognizes numerous organic compounds which can beused to inhibit the corrosion of metals subject to corrosive attack byaerated, aqueous solutions. Such inhibitors have been found to begenerally ineffective, or only slightly effective, for inhibiting thecorrosion of cop-per alloys contacted by aerated, aqueous solutions ofcommercial detergents.

It has been determined that this condition is due to the presence ofbuilders in certain detergent formulations, these builders beingalkali-metal polyphosphate salts, commonly sodium tripolyphosphate,sodium pyrophosphate, or sodium hexametaphosphate, or mixtures thereof.Normally, in the use of detergent compositions in machinery such asfound in laundries or factories, coatings of corrosion products andother insolubles form a protective layer on metal surfaces. The presenceof builders in detergents, however, prevents or removes this layer andpromotes corrosion of the metallic surfaces. It has been found that suchcorrosion can be effectively inhibited by incorporating in the aqueousmedium small amounts of naphthenic acids.

It is therefore an object of this invention to provide a novel methodfor inhibiting the corrosion of copper alloys contacted by aerated,aqueous, detergent solutions. Another object of this invention is toprovide a novel detergent composition for use in apparatus fabricated atleast in part of copper alloys. Other objects of this invention willbecome apparent from the following description.

In general, the naphthenic acids useful in this invention are obtainedfrom petroleum, and preferably will have an average molecular weight ofnot less than about 250 and an acid number not greater than about 190.Still more preferably, the naphthenic acids will have a molecular weightof about 330 to about 415 and an acid number of about 122 to about 159.Such naphthenic acids, when used in the amount of about 0.005 to 0.1percent by weight, in aerated, aqueous solutions of commercialdetergents containing polyphosphate builders are effective forinhibiting corrosion of copper alloys contacted by such solutions.

Copper alloys having normally high corrosion resistance, which arereadily attacked by aqueous, aerated, polyphosphate solutions includecopper-zinc alloys containing 60-90% by weight of copper, such asgilding metal, commercial bronze, red brass, spring brass, common brass,muntz metals, and admiralty brass. Copper alloys containing minoramounts of metal such as zinc, lead, tin, aluminum, and nickel such asforging brass, architectural bronze, aluminum brass, naval brass,nickel-aluminum bronze, aluminum bronze, and cupronickel are alsosubject to corrosive attack and can be inhibited in accordance with thisinvention. The alloys protected can also contain minor amounts ofmanganese, beryllium or phosphorus.

It has been found that the alkali-metal polyphosphate salts responsiblefor accelerated corrosive attack upon normally corrosion-resistantcopper alloys are the pyrophosphate, tripolyphosphate, hypophosphate,hexametaphosphate, and trimetaphosphate salts. Of these, thepyrophosphate, tripolyphosphate, and hexametaphosphate salts of sodiumare especially likely to be found in commerical detergents, and resultin serious corrosion problems when such detergents are employed inapparatus fabricated of copper alloys.

The effectiveness of the method of this invention for inhibitingcorrosion, as well as the ineffectiveness of a Wide variety ofchemically similar corrosion inhibitors of the prior art, for inhibitngthe corroson of copper alloys contacted by aerated, aqueous solutions ofcom mercial detergents has been demonstrated experimentally. First, aWater solution of a commercial detergent composition containing mixedaryl alkyl sulfonates, sodium tripolyphosphate, sodium sulfate, andother components (0.5 gram detergent per milliliters of water) wasprepared and divided into a plurality of flasks. Suflicient amounts ofvarious inhibitors were added to each flask to produce an inhibitorconcentration of 0.1 gram per 100 milliliters of solution. Finally, twobrass strips 6. inch by 3 inches) were immersed in the solutions in eachflask, and air was bubbled through the solutions at a rate of 2030milliliters per minute for a period of 72 hours while the temperaturewas maintained at about 70 centigrade. Percent weight loss from thebrass strips for each test are given in the following table.

The three naphthenic acids employed in the experiments reported in thisspecification are characterized as set forth in Table II.

Table II Naphthenic acid M01. wt. Acid number IBP F.) at

(mg. KOH/ 2 mm. Hg

gram) Number 1 207 178 315 Number 2. 330 159 287 Number 3 415 122 408 Afurther series of experiments was performed to establish that theeffective agents causing the corrosion of normally corrosion-resistantcopper alloys were polyphosphate builders usually employed in commercialdetergents. These further experiments also establish. that naphthenicacids when employed in the method of this invention are effective forinhibiting corrosion induced by the presence of polyphosphates inaerated aqueous solutions. in Table III.

The results of the experiments are set forth Table .III

Detergent components Component, Detergent, Inhibitor Inhibitor, PercentWt. percent wt. percent wt. percent Wt. loss DBSS 100 0.5 -0. 25 DBSS 40-0. 11 Sodium sulfate 6O DBSS; 40 Sodium sulfate 40 0. 5 0.07 YTrisodium phosphate 40 DB SS 40 Sodium sulfate 20. 1 0. 5 1. 04 Sodiumpyrophosphateflu 40 DBSS 40 Sodium sulfate 40 0. 5 N aphtlienic acidNo. 1. 0. 2 O. 41 Sodium pyrophospha 40 DBSS 40 Sodium sulfate 0 5 l. 33Sodium tripolyphosphate 4O DBSS 40 Sodium sulfate 20 0. d Naphtlienicacid No. L 0. 2 0. 28 Sodium tripolyphosphate 40 Sodium pyrophosphate100 0. 5 1- 75 Do 100 0. 5 Naphthenic acid N o. 1. 0.2 0.52 Sodiumtripolyphosphate 100 0. 5 1. 64

Do 100 0. 5 Naphthenic acid N 0. 1 0. 2 0. 34

l Dodecylbenzene'sodium sulfonate.

It will be 'noted that the naphthenic acids were not as effective ininhibiting corrosive attack upon copper alloys induced by the syntheticdetergent compositions of Table III. This is believed ,to be because ofthe abnormally high concentration of polyphosphates in the compositionsof Table III. In these experiments, the same procedure as described withreference to Table I were employed.

While the invention has been described with reference to commercialdetergent solutions based upon alkaryl sodium sulfonates and includingpolyphosphate builders, the method of this invention is useful ininhibiting corrosion produced by and detergent composition whichincludes polyphosphate builders.

This invention also contemplates and includes detergent compositions perse which employ polyphosphate builders and which include a small buteffective amount of naphthenic acids to inhibit corrosion of copperalloys which would otherwise occur when the detergent is placed inaqueous solution and contacts structures fabricated of copper alloys.Thus, the detergent compositions of this invention will include any of awide variety of cationic, nonionic, or anionic detergents which includea minor but effective amount of polyphosphate builders, and a smallamount of naphthenic acid inhibitor. Especially preferred compositionsare detergents based upon alkaryl sodium sulfonates, and including minoramounts, usually in the range of about 5-20%, of polyphosphate builderssuch as the alkali-metal pyrophosphate, tripolyphosphate,hexametaphosphate, trimetaphosphate, and hypophosphate salts.Preferably, the builders will be the sodium salts such as sodiumpyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate. Apreferred detergent base is dodecylbenzene sodium sulfonate. Thedetergent composition will contain about 120% by weight, and preferablyabout 5% by Weight, based upon the total weight of the detergentcomposition, of the aforedefined naphthenic acids.

A specific example of a detergent composition in accordance with thisinvention is as follows:

Percent Dodecylbenzene sodium sulfonate 75 Sodium sulfate 10 Sodiumpyrophosphate 5 Sodium tripolyphosphate 5 Naphthenic acid No. 1 5

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method of inhibiting the corrosion of copper-conacid number notgreater than about 178, said naphthenic acids comprising about 0.005 to0.1% by weight of said taining metals in contact with aqueous, aeratedsolutions j solutions.

2. The method in accordance with claim 1 in which said alkali-metalpolyphosphate salts are selected from the group'eonsisting of sodiumpyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate.

The'method in accordance with claim 2 in which said solution is adetergent solution containing alkaryl sodium sulfonates.

4. The method in accordance with claim 3 in which said sulfonate isdodecylbenzene sodium sulfonate.

5. .The method in accordance with claim 4 in which said naphthenic acidsare characterized by an average molecular weight of about 330 toabout'415, and an acid number of about 122 to 159.

6. A detergent composition consisting essentially of an alkaryl sodiumsulfonate, effective amounts of alkalimetal polyphosphate builders toprevent the formation of insoluble soaps by metathesis in the solutionsin which said composition is used and about 1-20% by weight of saidcomposition of naphthenic acids characterized as having a molecularweight of at least about 297 and an acid number not greater than about178.

' 7. The-composition in accordance with claim 6 in which said alkalimetal phosphate salts are selected from the group consisting of sodiumpyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, andmixtures thereof.

8. A composition in accordance with claim 7 in which said sulfonate isdodecylbenzene sodium sulfonate.

9. The composition in accordance with claim 8 in which said naphthenicacids are characterized by an average molecular weight of about 330 toabout 415, and an acid number of about'122 to 159.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES4 NACE Technical Committee Reports, (publication 55-3), NationalAssociation of Corrosion Engineers (vol. 11, pp. 65 and 67).

JULIUS GRE ENWA LD, Primary Examiner. I. T. FEDIGAN, Assistant Examiner.

6. A DETERGENT COMPOSITION ESSENTIALLY OF AN ALKARYL SODIUM SULFONATE,EFFECTIVE AMOUNTS OF ALKALIMETAL POLYPHOSPHATE BUILDERS TO PREVENT THEFORMATION OF INSOLUBLE SOAPS BY METATHESIS IN THE SOLUTIONS IN WHICHSAID COMPOSITION IS USED AND ABOUT 1-20% BY WEIGHT OF SAID COMPOSITIONOF NAPHTHENIC ACIDS CHARACTERIZED AS HAVING A MOLECULAR WEIGHT OF ATLEAST ABOUT 297 AND AN ACID NUMBER NOT GREATER THAN ABOUT 178.